The present invention relates to heat exchangers for semiconductor chips.
The dissipation of thermal energy away from a semiconductor chip has been a matter of concern which has generated a significant quantity of art in the field. As circuits have become more highly integrated, the amount of thermal energy generated by the circuits has increased. Thermal energy in a semiconductor chip will elevate the temperature of the chip, which in turn, decreases performance and reliability.
The problem of thermal energy is compounded when the semiconductor chip is position in a dense arrangement of computer circuitry in a circuit board. With the circuit board being disposed in a supportive and protective enclosure, along with adjacent circuit boards, the overall effect is to concentrate thermal energy around the chip.
When high levels of thermal energy are anticipated, heat dissipation may be best achieved by use of a fluid cooled heat exchanger. The small dimensional scale on which this must occur, and within the tight confines of an arrangement of circuit boards, presents unique problems in the area of heat exchange. For example, elaborate systems of fluid distribution through such exchangers to increase heat transfer efficiency are not feasible, as contrasted with large scale heat exchangers, where spatial confines are not nearly as much of a problem. Furthermore, expense per unit must be kept to a minimum as the number of exchangers needed through the circuitry of some computer systems will be large. In addition, mechanical problems of installation arise. Fluid cooling can be performed using an air flow over a chip or a heat exchange on a chip. Many computers have small fans on the inside to provide a flow of air over the circuits and components to enhance cooling. If a liquid, such as water, is used as the cooling fluid, the design of the circuit board becomes more complicated because cooling water must be run to each of the exchangers. The tight confines within which this must occur necessitates heat exchanger design that allows easy access to the exchanger with a fluid source.
The present invention provides a apparatus for improving heat transfer efficiency in the area of heat exchange for semiconductor chips as well as improving accessibility to the to the heat exchanger for providing fluid to the exchanger.
A cylindrical conduit chamber has inlet and outlet fluid conduits. The cylindrical conduit chamber has a bottom surface that mates with an annular wall extending from a fin plate. The bottom surface of the conduit chamber, the annular wall, and the fin plate define a circular chamber through which fluid is passed and into which heat is drawn from a heat emitting source.
The cylindrical conduit chamber is mounted within a retaining assembly for releasably attaching the heat exchanger to a semiconductor chip package. The cylindrical conduit chamber is rotatable within the assembly. As such, when the assembly is disposed in a circuit board, tubing is easily run to an opening of the inlet conduit on the cylindrical conduit chamber, since it can be rotated to face the direction from which the tubing is run.
The fin plate has a plurality of fins which are arranged in two concentric circular arrays. The fins are arranged in a generally radial array and have the shape of a spiral pattern. Each fin in both the inner and outer arrays of fins, extends laterally from a leading edge to a trailing edge which is radially outward of the leading edge. Each fin is curved to provide a spiral pattern in the array. The spiral pattern of the fins results in the trailing edge being rotationally offset from the leading edge. The fins can be curved or straight but are curved in the preferred embodiment. In addition, between the inner and outer array of fins there is an annular space. Similarly, between the outer array of fins and the annular wall, there is a second annular space.
The bottom surface of the cylindrical conduit provides an overhead wall of the circular chamber. A fluid inlet aperture is positioned above the center of the fin plate. A fluid outlet aperture is also positioned on the overhead wall, but above a peripheral portion of the fin plate. An annular fluid channel is recessed upwardly into the overhead wall. The annular channel of the overhead wall is disposed over the second annular space. The annular channel has a varying cross section area that decreases from a position furthest the outlet aperture and becomes a minimum at a position adjacent the outlet aperture.
The structure of the heat exchanger described provides a preferred embodiment of an apparatus for carrying out the method of heat exchange introduced by the present invention.
The structure allows for impacting the fluid on a central portion of a plate within a circular chamber to create turbulence in the fluid which results in an improved heat transfer coefficient. From the center region of the fin plate, the fluid disperses generally radially throughout the fluid chamber, being guided by the fins in a spiraling direction. When the fluid reaches the annular wall, it has a rotational velocity. The rotational velocity of the fluid about the perimeter of the chamber reduces back pressure against the fluid flowing radially outward. This improves fluid distribution.
The varying cross sectional area of the recessed annular channel, has the effect of equaling pressure drop for a given flow rate of fluid, initiated in any radial direction from the central region of the plate, on through to the outlet aperture. The resulting improvement is that fluid flow is evenly distributed throughout the chamber, rather than coming to a steady state wherein pressure is equalized such that most of the fluid flow is straight from the inlet aperture to the outlet aperture without traversing any portion of the second annular space.
The fins are curved in the preferred embodiment which changes the momentum of the fluid with respect to the fins as it passes by the fins, and this in turn, reduces boundary layer thickness on the fins. The result is an improved individual heat transfer coefficient of the fluid. The curvature also serves to provide extra surface area for heat transfer.
There is an annular space between the inner array of fins and the outer array. The annular space breaks off boundary layer formation on the inner array of fins such that it is re-initiated again at the outer array. This serves to minimize boundary layer formation.
An advantage of the present invention is that it provides optimum fluid distribution through the fluid chamber of the exchanger with relative simplicity. Furthermore, it provides easy access for running a fluid line to the exchanger, without having to use varying amounts of line depending on how the exchanger is configured within the board.